<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="utf-8">
    <title>类式组件 state</title>
</head>

<body>
    <button id="btn1">按钮</button>
    <button id="btn2">按钮2</button>
    <button onclick="demo()"> 按钮3</button>
    <script type="text/javascript">
        const btn1 = document.getElementById('btn1')
        btn1.addEventListener('click', () => [
            alert('按钮1被点击了')
        ])
        const btn2 = document.getElementById('btn2')
        btn2.onclick = () => (
            alert('按钮2被点击了')
        )
        function demo() {
            alert('按钮3被点击了')
        }
    </script>
</body>
</html>